Electronically controlled fuel injectors are well known in the art including both hydraulically actuated electronically controlled fuel injectors as well as mechanically actuated electronically controlled fuel injectors. Electronically controlled fuel injectors typically inject fuel into a specific engine cylinder as a function of an injection signal received from an electronic controller. These signals include waveforms that are indicative of a desired injection rate as well as the desired timing and quantity of fuel to be injected into the cylinders.
Emission regulations pertaining to engine exhaust emissions are becoming more restrictive throughout the world including, for example, restrictions on the emission of hydrocarbons, carbon monoxide, the release of particulates, and the release of nitrogen oxides (NOx). Tailoring the number of injections and the injection rate of fuel to a combustion chamber, as well as the quantity and timing of such fuel injections, is one way in which to control emissions and meet such emission standards. As a result, split fuel injection techniques have been utilized to modify the burn characteristics of the combustion process in an attempt to reduce emission and noise levels. Split injection typically involves splitting the total fuel delivery to the cylinder during a particular injection event into two separate fuel injections such as a pilot injection and a main injection. At different engine operating conditions, it may be necessary to use different injection strategies in order to achieve both desired engine operation and emissions control. As used throughout this disclosure, an injection event is defined as the injections that occur in a cylinder during one cycle of the engine. For example, one cycle of a four cycle engine for a particular cylinder, includes an intake, compression, expansion, and exhaust stroke. Therefore, the injection event in a four stroke engine includes the number of injections, or shots, that occur in a cylinder during the four strokes of the piston. The term shot as used in the art may also refer to the actual fuel injection or to the command current signal to a fuel injector or other fuel actuation device indicative of an injection or delivery of fuel to the engine.
In the past, the controllability of split injections has been somewhat restricted by mechanical and other limitations associated with the particular types of injectors utilized. In addition, in some embodiments, such as disclosed in the U.S. Pat. No. 5,740,775, the total fuel quantity associated with a split injection is apportioned such that approximately 50% of the fuel is associated with the first fuel shot and approximately 50% of the fuel is associated with the second fuel shot. Under the more restrictive emissions regulations of today, this fuel partitioning strategy yields higher than desirable hydrocarbons and excessive fuel dilution of the oil. Even with more advanced electronically controlled injectors, during certain engine operating conditions, it is sometimes difficult to accurately control fuel delivery, even when utilizing current control signals.
In addition, some spark ignited engines incorporate split injection fuel strategies, such as disclosed in the U.S. Pat. No. 5,609,131. However, in order to achieve desired ignition timing utilizing a spark or glow plug, these engines are restricted in the manner of fuel distribution among the shots, thereby reducing their effectiveness with regard to reducing engine emissions.
Desired engine performance is not always achieved at all engine speeds and engine load conditions using the previously known fuel injection strategies. Based upon engine operating conditions, the injection timing, fuel flow rate and the injected fuel volume are desirably optimized in order to achieve minimum emissions and desired fuel consumption. This is not always achieved in a split injection system due to a variety of reasons, including limitations on the different types of achievable injection waveform types, the amount of fuel injected during the pilot shot, when the two injections take place during the particular injection event, and the timing sequence between the two injections. As a result, problems such as injecting fuel at a rate or time other than desired within a given injection event and/or allowing fuel to be injected beyond a desired stopping point can adversely affect emission outputs and fuel economy.
It is therefore desirable to control and deliver any number of separate fuel injections to a particular cylinder including three or more fuel shots so as to minimize emissions and fuel consumption based upon the operating conditions of the engine at that particular point in time. This may include splitting the fuel injection into more than two separate fuel shots during a particular injection event, providing a specific fuel quantity relationship between the respective fuel shots in a particular injection event based upon the number of fuel shots associated therewith, advancing the pilot shot during the compression stroke, delivering the respective fuel shots within defined crank angle or cylinder piston displacement limits, and adjusting the timing between the various multiple fuel injections in order to achieve desired emissions and fuel consumption. In some situations, it is also desirable to rate shape the front end of the fuel delivery to the cylinder to control the burn characteristics of the particular fuel being utilized and, in other situations, it may be desirable to rate shape the tail end of the fuel delivery to the cylinder to achieve desired emissions control and engine performance.
Accordingly, the present invention is directed to overcoming one or more of the problems as set forth above.